The ear converts acoustic impulses into signals interpretable by higher centers. The delicate acoustic instrument, the organ of Corti (0C) is made of living cells with all their susceptibilities. Most dysfunctions of the ear are mediated chemically, and for medical reasons, it is Imperative that these biochemical mysteries be elucidated. This proposal considers the biochemistry and molecular biology of two proteins (OCPI and OCP2) of unknown function present in the 0C at exceedingly high concentrations. The large amounts, expression restricted to the inner ear, and major increase in expression at the time the cochlea begins to function imply an important role in audition. This dictates an aggressive interdisciplinary approach to elucidate their function. We will apply standard techniques of protein chemistry adapted to the micro level. Analysis of primary amino acid sequence will exploit recent technological advances. Cellular and subcellular localization by immunohistochemical techniques will provide indirect information about their function. Standard cloning techniques will provide fundamental insights into structure and function of the OCPs. More importantly, the proposed mRNA expression experiments use OCPs as a tool to obtain important information about inner ear development. Cloning human 0CP genes provides them as candidate genes for inner ear disease. A large body of preliminary information on these projects makes them high priority and low risk. The 0C resides in tissue culture, as it were, surrounded by fluids of fundamentally different chemical makeup and electrical polarization. A precise definition of the composition of these fluids is of paramount importance. We have designed sophisticated techniques to avoid artifacts in the determination of the chemical composition of perilymph. We will determine valid concentrations of numerous small molecules and establish comprehensive protein profiles. Most artifacts are due to influx of cerebrospinal fluid (CSF) whenever the otic capsule is perforated, either for the sampling of specimens or insertion of electrodes. The influx of CSF may damage the 0C, since it results in very low levels of amino acids, low protein, and other potential sequelae. This situation also exists in perilymph fistulae, and may contribute to the disturbance of hearing. Our studies are also geared to the study of perilymph- or disease-specific proteins, and will critically evaluate the claim that perilymph of scala tympani is derived in bulk from CSF.